1. Field of the Invention
The present invention relates to a construction of a thrust bearing for an adjustable blade shaft of an axial-flow fan with adjustable blades which swings at a relatively slow speed.
2. Brief Description of the Prior Art
The adjustable blade shaft bearing which supports a plurality of adjustable blades attached to an impeller hub around its outer periphery must support a heavy load of accessaries such as clamping nuts, arms and so on while lightly, smoothly acting when the adjustable blades are swung.
In order to satisfy the requirements described above, spherical thrust roller bearings are used. In order to prevent fretting corrosion due to small vibrations during the operation, the forced lubrication systems have been used. A typical example of the forced lubrication systems is disclosed in FIG. 2, at page 40 of Hitachi Hyoron Vol. 60, No. 5, published May 1978.
Oil supply and discharge holes are formed through a main shaft which supports an impeller hub, and one end of the oil supply hole the other end of which is connected to an oil supply device is connected to one end of a supply hole the other end of which opens to a spherical thrust roller bearing and which is formed through the impeller hub. The other end of the discharge hole is connected to the other end of another hole which is formed through the adjustable blade shaft and one end of which opens to the thrust bearing.
In the prior art system of the type described above, therefore, not only the machining of devices and parts required for forced lubrication is required, but also there arises the problem that the workability is extremely worse because of the spill of lubricating oil in the case of the disassembly of the adjustable blades.
Meanwhile, the thrust bearing is covered with a cover in order to protect the bearing surfaces from water, dust or the like, and if needs demand, lubricating oil such as grease is filled in the cover. This arrangement is well-known in the art from U.S. Pat. No. 2,230,668. Furthermore U.S. Pat. No. 3,937,300 teaches the provision of a lubricating oil cartridge at the end of a spline shaft, the cartridge being replaced with a new one when lubricating oil decreases.